Insulating compound



Patented Apr. 12, 1938 UNITED STATES PATENT OFFICE INSULATING CODIPOUNDNo Drawing. Application May 28, 1936. Serial No. 82,260

4 Claims.

This invention relates to insulating composition for use in fillingelectrical apparatus. subjected to high tension electric currents orstresses, and particularly for filling such equipment as "'5 potheadsand other terminals. This application is a continuation-in-part of mycopending application Serial No. 738,815, filed August 7, 1934.

In terminating a high tension cable, where itenters a power station orsub-station, or is connected to electrical apparatus, the cable isextended into a connecting apparatus of suitable construction where itis connected to electrical apparatus, bus-bars, or other equipment. Onetype of'connecting device is what is known as a pothead consisting of ametal body with a hollow porcelain insulating cover, through which theconductor is. passed to an overhead connection outside of the pothead.

After entering the pothead, the cable is generally stripped, orpartially stripped, of its wrapping of impregnated insulation, and tosupply the necessary insulation between the metal body and theconductor, the pothead is filled with an insulating composition,generally an asphalt, or similar material. Another type of terminalstructure is a junction box generally made of metal and containingbus-bars. and lateral connecting cables. These junction boxes may alsobe filled with an insulating composition to protect any exposedconductors from moisture or from grounding.

Cable splices and other constructions are also used at the terminals forcables.

Wherever apparatus of the above type has been filled with an insulatingmedium, it has usually been the practice to use asphalt, or similarbituminous material either plain or compounded with other liquefiableingredients. The asphalt has generally been filled into the pothead. orother metal container by melting it and pouring it into the container,permitting it to set therein.

Asphalts and compounds of like nature, which have heretofore been usedhave, in general, supplied a high dielectric strength, but they sufferedfrom the disadvantage that they have a high specific inductive capacity,generally higher than that of the insulation of the cable. Therefore,they tend to become overstressed in service. This is overcome to someextent by partially or fully insulating the exposed portion of theconductor within the pothead or terminal body by wrapping these exposedparts with tapes which requires a hand operation.

Moreover, the asphalt type of filling compounds must be melted in orderto be poured into the terminal body, usually through a small opening,thereby having a tendency to include condensate and. air in the fillingand cause electrical leakage and, eventually, failure. An obstacle alsoarises to filling certain forms of potheads or chambers owing to thetendency for the asphalt to rapidly chill and solidify before it canenter and fill the narrower passages. Also these asphalt compounds havea tendency to shrink when solidified, leaving voids which are sources ofweakness and points of potential failure.

An object of my present invention is to provide an improved fillingcomposition for electric'al apparatus, such as potheads and terminalstructures, which will have the required dielectric strength without anabnormally high specific inductive capacity and which is of such aconsistency as readily to fill the potheads or other structures and toavoid the formation of voids, etc.

The filling material of my invention comprises a pasty, pulpycomposition of fibrous insulating material such as paper pulp andinsulating liquid such as mineral oil or composition of mineral andother oil, such as resin oil, impregnating and filling the pulp. Thefibres are in a free substantially unmatted condition and may be moldedor packed into spaces to be filled, and the oil is in sufiicientquantity to fill the interstices. and spaces within the fibrous mass.

For impregnating a paper insulated cable, a mineral oil or a mixture ofabietic acid and oil is commonly used. and the same liquid insulation issuitable for forming the compound of my invention. In general, however,any impregnating insulating fluid used in the cable itself will besatisfactory as the filling or impregnating fiuid of my invention.

fibrous material may be in the form of a loose fluff of fibres havingabout the size and characteristics of a loosely fluffed paper pulp sothat the resulting pasty composition of insulating fluid or liquid andpulp may be readily filled or pressed into the pothead or othercontainer in which it is to be used. The quantity of pulp in thecomposition may be varied to give a result ing composition having adesired fluidity and may be governed to some extent by the particularoil or insulating fiuid being used and by the fibre density orcoarseness of the fibres used. Generally, the maximum quantity of paperpulp to be used with an oil of the type commonly used for impregnating apaper wrapped cable will be about 25% dry weight.

Smaller percentages, such as about 10% will,

in general, be a desirable proportion to use with the usual type ofpaper pulp.

As the composition is generally a pasty or pulpy mass, it may be readilyfilled into the containers and compacted therein and is not subject tothe formation of cracks, such as may happen upon the cooling of solid orrigid filling material.

The pulp of fibrous material holds the liquid in a fibrous network sothat it does not readily flow out of position. The fluidity of the oilis thereby checked. The mass of the pulp retains its ability to move andto alter its shape when pressed into position.

The pulp and liquid insulating composition of the above invention hasthe advantage that its dielectric properties closely approximate thoseof the impregnated paper wrapping of the cable itself. This isundoubtedly due to the breaking up of the dielectric paths by the fibresof the paper and in this way the dielectric properties are increasedover those of the insulating liquid itself.

Through the above invention, a sudden change in the specific inductivecapacity from the cable insulation to the filling composition within theterminal body is reduced to a minimum or entirely eliminated. By theproper combination of pulp and insulating fluid, the dielectric strengthof the filler compound in a direction radially of the conductor can bemade equal to or higher than the strength of the cable insulation.Moreover, the dielectric strength of the filler composition in an axialdirection will be of the same order as the radial strength because ofthe fact that there is no separating line, such as may be caused by thegelling of a liquefiable solid compound on either the terminal bodywalls, or the surface of the conductor.

Through the above invention, I have, therefore, provided a fillingcomposition of wide general use for insulating an electrical conductorfrom a surrounding spaced enclosing structure.

What I claim is:

l. A pasty filling composition consisting of a cable insulating oil anda fibrous pulp of nonconducting material immersed in said oil and beingnot over about 25% of the weight of the composition and the resultingmixture being fluid.

2. A pasty filling composition consisting of a cable insulating oilcomposition and paper pulp immersed therein, the paper pulp constitutingnot over about 25% of the total Weight of the composition and theresulting mixture being fluid.

3. A pasty filling composition consisting of a cable insulating oil oflow specific inductive capacity and a fibrous pulp of non-conductingmaterial immersed in said oil and constituting not over about 25% ofsaid composition and the resulting mixture being fluid.

4. A pasty filling composition consisting of a pulp of non-conductingfibrous material and an insulating fiuid consisting of a mineral oil andabietic acid penetrating and saturating said pulp, said pulp comprisingnot over about 25% by weight of said composition and the resultingmixture being fluid.

HAROLD F. ORMEROD.

